Precancerous lesions of the colon and rectum.

Fourty-six cases of polyps and polypoid lesions of the colon and rectum were operated at the First Department of Surgery, Gifu University School of Medicine during the last 16 years. Polyps were classified into five groups according to their degree of atypicality and the relationship between polyps and cancer was investigated. The adenomatous polyps were prone to become malignant and it appears that the larger the polyp size, the greater the incidence of severe atypia and the greater the polyps' malignant potentiality. The malignant polyps developed more frequently in the distal colon and rectum than in other parts. Focal and invasive cancers limited to the submucosal layer were found exclusively in the sigmoid colon and rectum.